Some vehicles, such as buses and natural gas transport trucks use liquid natural gas (LNG) as the form of fuel storage used on the vehicle. The LNG is vaporized and warmed before it travels to the fuel system on the engine. LNG tank systems include a heat exchanger to vaporize cryogenic LNG from the liquid to gaseous state. In the event of a loss of engine coolant supply or catastrophic failure of the heat exchanger, cryogenic fuel can flow to the fuel system and flow through many components that are not rated to endure cryogenic temperatures, leading to possible LNG leakage and fire risk.
Some current methods for preventing flow of liquid LNG rely on temperature sensors to detect changes in gas temperature or coolant temperature in the heat exchanger in order to detect LNG heat exchanger abnormalities. In the event that an abnormality is detected, a shut-off valve rated at a sufficiently low temperature is used to stop the flow of gas or LNG to the engine fuel system. Such cryogenic rated sensors and valves are typically expensive, and are sometimes unable to detect and react to all failure modes in time to prevent downstream issues. These types of methods are expensive and may not guarantee proper detection of an unsafe condition. There are very few, if any, cryogenic rated sensors or valves that are cost appropriate for the on-highway LNG market.